These vests are made to fit over jackets when they are adjusted to their largest position. If you choose not to wear the vest over a jacket then you can make the mid-torso area smaller with the side Velcro adjustment straps. Even considering that Icon size estimates are given assuming you are wearing the vest over a jacket, we find the fit estimates to be very generous. Below, we are listing maximum and minimum mid-torso measurements (about half way between your chest and your waist). The cut of the vest will accommodate a wide range of chest sizes since the arm holes are cut very deep. You can use a tape around yourself while wearing a jacket and also without a jacket and make a size choice based upon the chart.